1. Field of the Invention
The present invention relates to a new and improved method and apparatus for separating oversize and on size particles in a mass of particulate material which is passed through a screening apparatus.
2. Description of the Prior Art
In accordance with the prior art, most vibrating screens are mounted with the screen cloth at a slope angle of from 15.degree. to 30.degree. above the horizontal. The material is passed over the upper surface of the screen from top to bottom usually under the influence of gravity alone and the flow is relatively slow because of the relatively shallow angle. The particles that are much smaller than the openings in the screen cloth easily pass through the screen mesh with little difficulty and similarly, the particles that are substantially larger than the screen mesh openings are positively rejected and do not pass through the mesh. These oversize particles move readily along and are eventually taken off the lower end of the screen as oversize. The main problem with prior art screening devices of the character described occurs with the particles of a critical particle size range wherein the particles are just slightly greater in size than the openings in the screen cloth. These critical size particles tend to fall into the open mesh, but because they cannot pass through the openings they become wedged solidly in the mesh causing the screen cloth to become blinded or plugged up. When this occurs, the screening operation is highly inefficient and as more material is passed across the screen, repeated collisions causes the particles to become wedged even more firmly. Cleaning of the screen cloth is then required before operations can be efficiently maintained.
In accordance with the present invention, however, the problem of blinding or wedging of critical size particles in the screen cloth openings is greatly reduced or entirely eliminated and the screening action is greatly speeded up.
It is an object of the present invention to provide a new and improved separating device and method for separating oversize from on size particles in a mass of particulate material flowing across a screening apparatus.
More specifically, it is an object of the present invention to provide a new and improved screening apparatus wherein blinding or wedging of particulate material in the screen openings is not a significant problem.
Another object of the invention is to provide a new and improved screening apparatus wherein particulate material is handled at a rapid rate and in a highly efficient manner.
Still another object of the invention is to provide a new and improved method and apparatus for screening material wherein the openings in the screen mesh are dimensioned to be considerably larger than the desired maximum on size particles with less chance of plugging up or blinding of the screen cloth yet with little or no oversize particles passing through the screen mesh.
Still another object of the present invention is to provide a new and improved screening apparatus wherein the screen mesh is supported at a relatively steep slope angle thus minimizing the possibility of critical sized particles tending to wedge or lodge in the slightly smaller sized screen openings causing the screen cloth to blind or plug up.
Yet another object of the invention is to provide a new and improved screening apparatus having a shield for rebounding the particles which bounce away from the screen cloth back toward the screen so that on size particles have numerous chances to pass through the openings in the screen.